Water softening with ion exchange material, such as resin particles or the like, is well known in the art. During the softening process, typically called the service cycle, the ion exchange resin particles acquire hardness inducing ions from raw water which is being treated in exchange for soft ions (i.e., ions which do not induce hardness to water). After continued contact of the resin particles with hard raw water, the particles' ion exchange capacity is considerably diminished and regeneration of the resin particles must be accomplished, conventionally by contacting the resin particles with a brine solution (i.e., an aqueous solution of sodium chloride or potassium chloride or the like) during a regeneration cycle.
The ion exchange process, which takes place during the regeneration of the ion exchange material, is accomplished in a softener or resin tank of well known construction. A separate brine tank is conventionally used to form brine for use during the regeneration cycle. When regeneration is initiated in the softener system, brine drawn from the brine tank passes through the bed of ion exchange material in the softener tank to reverse the exchange of ions and revitalize the bed by removing hardness inducing ions and replacing them with sodium ions, for example, from the brine.
The amount of brine which is required to regenerate a bed of ion exchange material of a predetermined volume, is dependent upon the extent to which the bed is exhausted during the service cycle. This, in turn, is dependent upon a number of factors, including: (1) the hardness of the water being treated; and (2) the quantity of water treated during the service cycle. The cost of operating the softening system may be reduced by limiting the amount of salt utilized in each regeneration cycle and the frequency of regeneration cycles to only those necessary to regenerate the resin particles.
Most water softeners are designed to regenerate on a predetermined timed cycle that is determined by taking into consideration the above-mentioned factors. The water softening system regenerates itself on the predetermined time cycle even if the water softening system is subjected to either an abnormally high or low usage during a particular period of time. In the instance of abnormally low usage, a waste of salt and water results. In the instance of abnormally high usage, the water softening system is unable to adequately soften all of the water passing through the system.
Many control systems have been proposed to take into account water usage on a real time basis. Such systems have been based upon means which detect the state of exhaustion of the resin bed or means which measure the quantity of water which has passed through the resin bed since the most recent regeneration cycle.
Systems which attempt to detect the state of exhaustion of the resin bed are disclosed in U.S. Pat. Nos. 3,246,759 and 4,257,887. These systems utilize electrodes, mounted in the resin bed, which are connected to a circuit which detects the condition of the resin bed. When the condition of the resin bed is such that rejuvenation should occur, a control circuit is activated to start the regeneration cycle. These systems, which rely on the difference in conductivity between beds of exhausted and rejuvenated resin particles, have not been completely reliable, are relatively expensive, and may result in salt usage that is not always in direct proportion to the volume of water processed.
One example of a softening control system that utilizes a means to measure the quantity of water that has passed through the bed is disclosed in U.S. Pat. No. 3,687,289. This system utilizes a metering device associated with the soft water line to draw off a predetermined proportion of the water flowing from the soft water line. The drawn-off water is directed to a pump chamber having an adjustable water storage capacity. The amount of water drawn off from the soft water line is directly proportional to the storage capacity of a pump chamber. The water stored in the pump chamber is periodically directed to the brine storage tank. The brine storage tank includes means to activate a timer when the water level in the brine tank reaches a predetermined level to signal the need for regeneration. The predetermined proportion of water drawn off is adjusted dependent upon the hardness of the water being treated.
The above discussed water softener system signals a regeneration after the usage of a predetermined amount of soft water. However, the regeneration cycle is usually delayed so as to occur at night. Therefore, the resin bed must have a reserve capacity to provide soft water for the remaining portion of the day after the need for a regeneration is signaled. The reserve capacity is typically selected to be that remaining after approximately 70% of the capacity of the resin bed is used. This large reserve capacity is needed to maintain soft water service in the event that the need for regeneration is signaled early in the day. Although such water softener systems may be designed or adjusted to vary the reserve capacity of the resin bed, once determined, the reserve capacity becomes fixed.
Another known water softener system utilizes a micro-computer to adjust the reserve capacity from day to day in response to soft water usage. The system includes a turbine water meter that measures the quantity of water passing through the resin bed. Based upon the quantity and hardness of the water that has passed through the resin bed, the micro-computer calculates the percentage of the capacity of the resin bed used since the last regeneration. The micro-computer employs an algorithm to make calculations and decisions based on accumulated time and water use. The algorithm allows a large reserve for days immediately following a regeneration and reduces the amount of reserve capacity as more days of significant water usage accumulate since the most recent regeneration. At such time as the reserve capacity for a day is reached, the water softener is scheduled for regeneration that night with a preselected fixed quantity of salt.
A system similar to the just described system utilizes a similar algorithm with additional criteria for reducing the probability of actual usage exceeding the variable reserve. This system determines and stores water average usage for each particular day of the week. At the end of each day, the calculated reserve capacity remaining in the resin bed is determined and compared with the stored water usage average for the next day. If the reserve capacity remaining is not adequate to meet the expected demand on the next day, the water softener is scheduled for regeneration that night with a preselected fixed quantity of salt.
The just described micro-computer systems utilize a variable reserve capacity and are able to schedule regenerations more in proportion to water usage and to thereby more accurately reduce the reserve capacity of the resin bed at the time of regeneration. However, both of these systems use a fixed quantity of salt for each regeneration. That is, the quantity of brine solution directed through the resin bed is the same during each regeneration. Accordingly, in instances where the reserve capacity of the resin bed is relatively high at the time of regeneration, a greater quantity of salt is passed through the bed than is necessary to rejuvenate the resin particles in the bed. As a result, salt is wasted.
Yet another method and system for regeneration of a water softener were disclosed in U.S. Pat. No. 5,544,072. This method and system had a default operating capacity and corresponding salt dose at midrange capacity. Since the majority of applications have relatively low hardness in relation to the capacity of the softener used, the actual operating capacity is typically adjusted downward to improve the overall salt efficiency of the softener. The result of starting at the midrange operating capacity, causes the softener to use more salt then necessary, at least initially.
The method also calculated the average percentage of capacity used for each day of the week to predict whether or not there is enough capacity remaining in the softener to cover the water usage required for the next day. The method reserves the next day's daily average plus an additional 50% of the daily average (i.e., the daily average*1.5). For example, if on a given day the average percent of capacity used was 40%, the patent will reserve 40%*1.5, or 60% for that days usage.
While this system and method works, in operation, the assumption to use an additional 50% of the daily average can over or under reserve the amount of the capacity needed in many instances. For example, if the consumer uses a very constant amount of water such as an average of 40% per day, the method and system will reserve 60% for that day, but it would only need to reserve 40%. If a softener had 45% of its capacity remaining, the additional reserve would cause the softener to regenerate prematurely, wasting regeneration water, and salt. In a second example, if the consumer uses 10% of the capacity on a given day, one week later the consumer uses 90% of the operating capacity, and this pattern is repetitive, then the average capacity for that given day of the week is 50%. The patent would reserve 50%*1.5 (or 75%) for that day. If the softener had 76% of its capacity remaining the day before the 90% usage day, it would not regenerate. That would mean the customer would have hard water the next day amounting to 14% of operating capacity.